If new parts are coming just pitch the old ones.IANAL but pretty sure it not being assembled doesnt matter to that alphabet soup. Its called Constructive Possession. The only way to stay legal would be to keep the parts physically separate so its not possible for you to assemble it into an NFA item. Like put the bad parts in a bag and give it to somebody to hold, take it to the office and put it in your desk/locker, etc.
But I wouldnt sweat it. You're more likely to win the lottery than have them chase you down over something so trivial.